Cushion mounting

ABSTRACT

A cushion mounting comprising a housing containing a liquid and a solid material having a bulk modulus of elasticity lower than that of the liquid. A load-carrying member is provided for supporting a load. The load-carrying member is mounted to reciprocate with respect to the housing so that the load-carrying member displaces some of the liquid so as to stress the liquid and solid according to the amount of displacement.

United States Patent Henderson Dec. 4, 1973 CUSHION MOUNTING 3,070,363 l2/l962 Ellis, Jr 267/35 [76] Inventor: Homer I. Henderson, 2220 Live Oak St., San Angelo, Tex.

Pnmary Exammer--James B. Marbert [22] Filed: Feb. 10, 1972 [21] Appl. No.: 225,311

Related U.S. Application Data [57] ABSTRACT [63] Continuation-impart of Ser. No. 12,589, Feb. 19,

1970, which is a continuation of Ser. No. 768,573, Aug. 19, 1968, abandoned, which is a continuation of A cushlon mountmg compnsmg a housing comammg Ser. No, 542,491, April 14, 19 abandoned, a liquid and a solid material having a bulk modulus of elasticity lower than that of the liquid. A load-carrying [52] U.S. Cl. 267/35, 267/65 R member is provided f pp g a lo The l [51] Int. Cl. B60q 11/62 y g m m is m e to r ipr with re- [58] Field of Search 269/35, 65 spec! to the housing so that the rrying m m displaces some of the liquid so as to stress the liquid [56] References Cited and solid according to the amount of displacement.

UNITED STATES PATENTS 3,380,729 10 Claims, 4 Drawing Figures 4/1968 Hofi'man et al 267/35 PATENTEU 41975 VOLUME IN N FIG.4

SHEET 1 UP 2 k ll AV [1 Ail/A H Al/ 11 Al I JNVENTOR.

HOMER l. HEN E SON CUSHION MOUNTING This invention relates to cushion mountings generally, and more specifically to a cushion mounting that has a high coefficient of damping and is a continuationin-part of my copending, similarly entitled U. S. Pat. application Ser. No. 12,589, filed Feb. 19, 1970, which was a continuation of my abandoned similarly entitled U.S. patent application, Ser. No. 768,573, filed Aug. 19, 1968, which was a continuation of my abandoned similarly entitled U. S. patent application, Ser. No. 542,491, filed Apr. 14, 1966.

The present invention incorporates in a single unit both impact absorbing and damping facilities. A cushion mounting is provided in which a liquid spring comprises a cylinder containing both a liquid and a solid material having a bulk modulus of elasticity lower than that of the liquid. This combination has many advantages over the 100 percent liquid spring such as: (1) reduced pressure modulus and spring modulus permits the use of large diameter piston rods; (2) the spring modulus can be changed simply by changing the percentage of solid to liquid; (3) reduced inter-cylinder pressure for a given impact which substantially reduces sealing problems and lowers cost and weight; (4) longer piston rod travel for a given impact which results in substantially less deceleration shock, and more liquid movement, yielding more dynamic fluid damping; (5) moderating the objectionable positive temperature coefficient of the liquid; and (6) the ability to prestress the spring for abnormally high loads by the introduction of additional liquid under pressure.

One object of this invention is to provide a low-cost, simple, trouble-free device that not only absorbs impacts and shocks, but also damps vibration. Another object of the present invention is to provide a liquid spring having a relatively low bulk modulus. Another object of the invention is the provision of a cushion mounting that permits a stroke for the full length of the device and with a substantially constant spring modulus. Another object of the invention is to provide a cushion mounting wherein the spring modulus is substantially constant but can be varied in use, over a wide range of values, resulting in either short stroke absorption of impact energy with high deceleration or alternately a long stroke absorption of impact with quite low deceleration. Yet another object of the invention is to provide for a wide range of damping coefficients, from quite low to quite high. Still another object of the invention is to provide a cushion mounting that can be used in series-reversed relationship to permit faster, and smoother damping of oscillation. Another object of the invention is the provision for varying quickly and easily the load-carrying faculty of any unit without dismantling it, or even unloading it. Another object of the invention is the provision of gauge means to indicate the static load, or impact force, on the cushionmounting. Finally, an object of the invention is to provide cushion mountings for use with lightweight objects, such as delicate instruments, or for heavy objects, requiring long strokes, such as aircraft.

The above objects, advantages, and features of the present invention, as well as others, are accomplished by providing a cushion mounting comprising a housing having means defining a chamber. The chamber contains a liquid and a solid material having a bulk modulus of elasticity lower than that of the liquid. A loadcarrying member is provided for supporting a load. The load-carrying member is mounted to reciprocate with respect to the housing so that the load-carrying member displaces some of the liquid so as to stress the liquid and solid according to the amount of displacement.

For a fuller understanding of the nature and objects of the present invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein:

FIG. 1 is a longitudinal sectional view of the present invention; 7

FIG. 2 is a top view of the invention taken on the plane 22 of FIG. 1;

FIG. 3 is a longitudinal sectional view of a modified form of the invention showing two cylinders working in series-reversed relationship; and

FIG. 4 is a graph showing the compressibility of examples of the liquid and solid material utilized in the present invention.

Referring now to FIG. 1 in greater detail, there is shown a cushion mounting in accordance with the present invention. It comprises a cushion mounting 10 in which a piston rod 19 operates. The mounting 10 comprises a cylinder 13 clamped between an upper head 1 l and a lower head 12 by tie rods 14. The cylinder 13 is hydraulically sealed to the heads 11 and 12 by O-rings 15. The piston rod 19 reciprocates through a seal-plug 20. The seal-plug 20 is threadedly secured within the upper head 11. The seal-plug 20 forms a seal with the head 11 by an O-ring 23. The piston rod 19 forms a seal with the seal-plug 20 by a lower U-ring 22, and an upper U-ring 21 which also serves as a scraper for piston rod 19. The U-rings 21 and 22 each have an inner surface of low-friction material such as teflon. The piston rod 19 is normally made as friction-free as practical such as by plating with hard chrome and polishing to achieve a highly polished surface. The seal-plug 20, may be made of a material having a low coefficient of friction, such as brass. The portion of the piston rod 19 which does not enter the seal-plug 20 (not shown) may be protected with a dust-boot in a conventional manner.

Within the cylinder 13 resides one or more cylinders of cork, or cork-like material 17. These cork cylinders may be cemented to the cylinder 13. The inner bore and ends of the cork cylinder may be coated with a film which may be an elastomer, such as urethane to protect it from abrasion. If damping is desired, a metallic damping tube 16 is mounted within the cork cylinder as shown. This tube 16 should be of a metal that conducts heat readily and should have a large number of small holes 18 to permit passage of fluid. The piston rod 19 has a cylindrical piston 28 that slidably fits the inner bore of the tube 16. The upper head 1 1 has a conventional oil filler fitting 24 with a passage 26 communicating with the inner chamber of the cylinder 13. The fitting 24 has a ball 25 which is spring pressed against a seat to retain pressure within the cylinder 13. The

lower head 12 carries a similar fitting 24 as well as a pressure gauge 27 both with passages 26 communicating with the inner bore of the cylinder 13. The lower head 12 may be mounted on a base 29.

Due to corks low coefficient of heat conduction, annular spaces 34 are provided so that oil can circulate and carry heat to the wall of cylinder 13. In instances of severe constant operation, it may be necessary to provide an additional means to conduct heat to the dissipating walls of cylinder 13. This may be in the form of a perforated disk 35, which disk should be of a metal with a high coefficient of heat conduction such as copper or brass. This disk may be secured by a press fit to the cylinder 13, and installed before cementing the cork cylinders 17 in place. In most applications this heat conducting disk 35 will not be required, and in such cases the two cylinders of cork shown in FIG. 1 are combined into one cork cylinder per unit, as will be described in FIG. 3.

The assembly of the device is fairly simple as will now be described. All sealing rings 15, 21, 22, and 23 are inserted in their grooves. The base 29 is set up, with the lower head 12 upon it. The cylinder 13 and damping tube 18 are then inserted in their respective recesses in the lower head 12. The piston rod is inserted in the seal-plug 20 and the seal plug screwed into the upper head 11. The upper head 1 1 is then positioned over the cylinder 13 and damping tube 16 and tie rods 14 are then inserted and tightened. The fittings 24 and gauge 27 are then inserted and tightened. The chamber of the mounting is then ready to be filled with liquid. Almost any chemically inert liquid is suitable, but oil is preferably used. If a great deal of damping is desired, the oil should be viscous otherwise non-viscous. By way of example, the oil should be a petroleum oil or a silicone oil of the type generally used in liquid springs. The oil is inserted by a pump through the lower fitting 24. As the oil is inserted, the ball 25 of the upper fitting is depressed to permit air to escape. Oil is pumped in until all of the air is exhausted. The cylinder 13 should be tilted and maneuvered until it is certain that all of the air is out, as any remaining air may cause foaming of the oil, and it will change the spring modulus of the mounting. The mounting 10 is normally left with zero oil pressure within the cylinder 13, except for the elevational head of the oil, which is normally negligible. The oil pressure can later be adjusted to accommodate the static load and with the piston rod 19 at any desired postiion.

The operation of cushion mounting 10 of FIG. 1, assuming that its sole purpose is to stop impacting objects, and/or to support loads, and that damping is not important, is as follows. When damping is notimportant, the perforated cylindrical damping tube 16 may be omitted or if retained for purposes of guiding the piston 28, the holes 18 are of large diameter. Assume that the load to be carried by the unit is 1,000 lbs., which is a mass of 1,000 32.2 31 slugs. Assume that the piston rod is 2 inches in diameter (3.14 in crosssectional area). Now the static force on the piston rod is solely this 1,000 lb. weight and the static pressure in the cylinder needs to be 1,000 lb. 3.14 in. 318 psi.. To provide this pressure, oil is pumped in the lower fitting 24, further straining the oil-cork composite until this pressure is reached, with the piston 28 in the position desired, and the piston rod 19 supporting the 1,000 lb. weight. Any excess pressure will tend to raise the piston rod 19 out of the cylinder 13 and any deficiency of pressure allows the piston rod 19 to enter further into the cylinder 13. This balancing or static pressure is indicated by the pressure gauge 27. This gauge can be calibrated in pounds of weight, if desired, and can be used to weigh the static load on the unit as well as the impact forces. Actually the amount of oil in the cylinder can be varied at will for an optimum piston rod 19 position as loads are varied. Wih the static load initially balanced, and with the required pressure inthe cylinder 13, any subsequent downward momentum of this load will impose an additional dynamic, downward impact force, causing a further intrusion of piston rod 19 into cylinder 13 with an increase in strain of the oilcork composite, and therefore an increase in pressure within the cylinder. This increased dynamic strain energy is stored in the oil-cork composite, and it not only stops the downward momentun, but it is at once expended in returning the piston rod to its static level, in a true resilient spring manner; hence the name liquid spring.

To compute the spring modulus and characteristics of the cushion mounting 10, assume that the piston rod 19 is 2 inches in diameter, thereby having a crosssectional area =3. 14 m3. Assume that the average cross-sectional area of cork and oil in the deviceis 10 times the area of the piston rod 19 or 31.4 in.. When the load is impacted and moves downwardly, impact forces are imposed upon the piston rod 19 as represented by the arrow 30, and this additional force causes the piston rod 19 to intrude still further into the cylinder 13. The base 29 resists the force 30 with forces 31, so that there is no movement of the cushion mounting 10.

Assume first, that there is only oil in the cylinder 13, no cork. As the impacted piston rod 19 moves into the cylinder 13, it subjects the oil to bulk compression. The bulk modulus of elasticity is computed from test data: K V P/ V, where V is the original volume, and v is the change in volume due to the increase of pressure, P. In using this equation the P is normally changed to P and rearranged to: P K v/ V for oil may be approximately 735,000 psi calculated at relatively high pressure (see page 189 of the well known text University Physics, 2nd edition, by Sears and Zemansky). At pressures between approximately 0 to 20,000 psi, the bulk modulus of elasticity for oil is approximately 328,000 psi, as given in Hydraulic & Pneumatic Power & Control by Franklin D. Yeaple, published by McGraw-Hill, page 5. The cushion mounting of the present invention is also suitable for operation at lower pressures characterized by a lower value of bulk modulus but for illustrative purposes the following computations will be made using the 735,000 psi figure as the bulk modulus of oil. The bulk modulus of elasticity K is computed in equation (1 above. Rearranging this equation to determine the pressure generated when the piston rod 19 inu'udes into the cylinder 13 (pressure modulus AP).

If the length L of cylinder 13 is 12 inches and the pisgm rod 19 intrudes 12 inches, thepressure modulus of piston rod 19 intrusion. To obtain the force or spring modulus S, it is necessary to multiply this by the area of piston rod 19:

S 73,500 X 3.14 231,000 lbs/ft. of intrusion 3 Hence, the initial intrusion of the piston rod 19 due to a static load of 1,000 lbs. is 1,000/231,000 0.00433 ft. There is, of course, an expansion of the steel cylinder 13 which depends on the thickness of the cylinder walls. These walls allow the cylinder 13 to expand more due to hoop stress, thereby increasing the volume of the cylinder 13 making the composite system softer. However, n r a Slight P sses it a t se modulus of steel of 30 million psi, the modulus ratio of steel to oil is approximately 40:1 (2.4 percent).

To compute the intrusion of the piston rod 19 due to impact forces, the formula F M A is used where F is force in lbs., M is mass in slugs, and A is the acceleration. In this case, A is deceleration which is negative. Also F S X where X is the intrusion of the piston rod 19 in feet. A may be represented as dv/dt, the rate of change of velocity with time whereupon the formula becomes:

M (dv/dt) and since dv/dt (dx dv/dt dx) V (dv/dx) (5) 5X dX MV dv. (6)

Assume the load of 1,000 lbs. is moving downwardly at 5 ft./sec and substituting constant values in equation (6) and integrating, using as limits the condition wherein the mass comes to rest: X 0.058 ft. or 0.696 inches. The maximum deceleration force generated is 0.058 X 231,000 13,400 lbs. The increase in pressure generated equals 0.058 X 73,500 4,270 psi. The time to bring the mass to rest is approximately X:- v/2 or 0.058/2.5 0.023 sec. 7

The maximum deceleration occurs at maximum force or at full stroke: 13,400/l,000 13.4g. This results in an abrupt stop with high pressure which is quite undesirable.

The insertion of even a small percentage of cork materially changes the characteristics of the cushion mounting 10. This change is due to the characteristics of cork and other materials having similar characteristics to cork. The important physical properties of a cork type material are: (l) buoyancy, (2) compressibility, (3) resilience, (4) resistance to moisture and liquid penetration, (5) closed cell construction, (6) negative temperature coefficient with respect to bulk modulus, (7) frictional quality, (8) low thermal conductivity, (9) ability to absorb vibration, and (10 stability. Most important to the operation of the present invention are the properties of very low bulk modulus of elasticity, imperviousness to liquid, closed cell construction wherein each cell is filled with air under pressure, and negative temperature coefficient bulk modulus-wise. Cork has long been used as a vibration absorber under heavy machinery and between the truck and car body of railroadfreight cars because it is extremely resilient under compression. At 750 psi cork is compressed to approximately one-half its original volume, and at 2,000 psi, it is compressed to one-quarter of its original volume. The negative temperature coefficient bulk modulus-wise of cork makes it very suitable for use in liquid springs. This means that cork expands slightly upon heating and its compressibility is greater at higher temperatures. Therefore, the higher the temperature the lower the bulk modulus of elasticity. This is a rather surprising property since cork is approximately 70 percent air, with 200 million closed cells per cubic inch. However, it is due to the substance suberine that composes the cell walls of cork. Like many organic materials, suberine is more rigid at low temperatures and less rigid at higher temperatures.

FIG. 4 shows graphically the relatively great com pressibility of cork. At 1,000 psi FIG. 4 shows the percent cornp'rss'ion o f oTsKflT llml .665 '60 percent. The compression of oil at a like pressure: Av/ V percent for a ratio of: 60/0.333 180/1. Cork has a much lower bulk modulus of elasticity than materials such as rubber. Engineering Materials Handbook 1st ed., by C. L. Martel], gives the bulk modulus of elasticity of rubber as 289,000 psi.

It is known that there is practically no diffusion of gas through the cell membrane of cork even when retained under extreme compression for long periods of time, such as when compressed for years as a stopper in champagne bottles. Fortunately, for this application its Poissons ratio is quite low, compared to other materials,-there being very little extrusion when it is compressed between two plates, as in a vise. The thermal coefficient of expansion of both cork and oil is relatively low. Therefore, there is a very minor variation of this cushion mount characteristics with temperature change. This variation is almost negligible when compared to gas-filled cushion mounts.

Assume now as in FIG. 1 that a cylinder of cork 17 is included in cylinder 13 comprising 10 percent of the interior volume of the cylinder 13, leaving percent oil. The change upon adding cork is due to its low bulk modulus of elasticity of 1,665 psi which remains substantially constant up to a pressure of 1,000 psi. Above 1,000 psi the bulk modulus of elasticity of cork changes with pressure but in the cushion mounting 10 the pressure will rarely exceed 1,000 psi. The bulk modulus for the combination of cork and oil is given by:

where K is the composite bulk modulus elasticity for oil and cork, K is the bulk modulus for cork, K is the bulk modulus of elasticity for oil and z is the percentage of cork the reciprocal UK is used here as this is the compressibility. Therefore, when the condition is 90 percent oil and 10 percent cork:

i. a. Koc 1 l p.s.i. (l,065) (732,()0O) giv'eEa' new fli''ssutfirsdiiuss i P= 16,300 (12 x 3.14)/12(31.4) 1,630 psi per foot of intrusion. 10

cylinder above where maximum deceleration was 13.4 g. and the time to bring the mass to rest was only 0.023

sec.

As larger percentages of cork are used, the pressure the liquid by the piston action. When considerable damping is desired, the damping tube 16 is used and holes 18 are small and quite numerous. This tube 16 may be of a permeable sintered metal. The friction loss modulus becomes less and less. Consequently, the in orifice flow is proportional to the velocity squared, static intrusion due to the 1,000 lb. weight becomes which is one reason for small holes. A second reason is greater and greater. For instance, with percent cork the increase in surface friction due to the large increase the pressure modulus .is 1,630 psi and to balance the of wetted area as the holes become smaller. The piston ll). WQl gl1 I I V llg ht 3;fa'f fl ,000/ 3,14 318 28 fits snugly in the damping tube 16. As the piston 28 psi is needed, which gives, therefore, an intrusion of 10 moves down, or up, it forces avolume ofliquid to move 3 18/1 ,630 0.195 ft. In any case, the static position of out of the tube 16, in front of it, and a volume to move the piston rod 19 can be placed at any point in its into the tube behind it, providing a dual effect whose stroke by regulating the amount of oil which in turn dedamping magnitude can be quite large. The velocity termines the pressure in the cylinder 13 as explained given tohe liquid is proportional to the time rate of above. travel of the piston rod 19. Therefore, there is much By varying the percentages of cork and oil, the folmore damping with initial large impacts than after lowing data in Table I results. In each case the load these impacts have been substantially stopped, or when i5 1 000 lb s thg gwg fq velo ityif 5 (l /Egg {he initially small. Of course, there is a pressure build-up piston is 2 inches in dia., (3.14 in. area) and the crossahead of the piston 28 and some pressure reduction besectional area of the oil cork is 31.4 in hind it. This absorbs some shock and reduces some- TABLE I Percentage oil and cork Max. dynamic Bulk mod. =K Length of Spring mod.=S Decelerating pressure increased Approx. time for Max. decelera- Oil Cork (p.s.i.) cylinder (ft) (lb/ ft.) piston travel (ft) (p.s.i.) deceleration (sea) lion (gs) This table gives an indication of the wide range of deceleration available with this device. To achieve softer deceleration and hence, a longer travel time, there are several alternatives: (1) reduce the composite bulk modulus by increasing the cork percentage, (2) decrease the ratio of piston volume per foot to the total cork-oil volume, or (3) increase the cylinder and stroke lengths.

A load having a mass M, falling onto the piston rod with a velocity V, has a kinetic energy of A M V. When there is no dynamic fluid damping this kinetic energy must be absorbed as strain energy in the oil-cork composite, and this is over and above that strain energy required to statically support the mass M; therefore the piston rod intrudes further than required for the static support of the mass M, it over shoots; but it is at once returned to its static support position by the expenditure of that quantum of strain energy stored solely by the kinetic energy and the piston rod comes to rest at the static support intrusion position. The strain energy required to statically support the load is still stored in the oil-cork composite. When dynamic damping is utilized the kinetic energy is dissipated as heat.

The above data assumed no damping, i.e.,- the damping tube 16 was either missing or, if present, the holes 18 were so large and numerous that there was no ap preciable liquid flow friction loss. Of course, there would be some friction loss due to molecular friction in the stress trained cork and oil, as well as some friction loss in the relatively low eddy flow pattern induced in what the pressure developed on the oil and cork outside of the damping tube 16. A high degree of damping reduces considerably the possibility of a destruction high energy rebound of the sprung weight. These factors must be considered when designing the unit for a given condition. FIG. 1 shows both ends of the damping tube free of holes for a short distance R. This is an optional feature whose purpose is to cushion with an almost total fluid compression any excessively large impact or rebound that would otherwise result in a metalto-metal stop. Some liquid would pass, depending upon the clearance of the piston and therefore it is not completely a liquid compression.

Regardless of how much damping is or is not achieved, the piston rod 19, for a given and load will be returned to its normal static loaded position by the kinetic strain energy stored in the cork and oil. The energy loss to heat due to kinematic flow of the oil is just that much less energy to be stored in strain energy in the oil-cork, and this energy is lost from the system as the heat is dissipated. Nearly all liquids are percent resilient with no apparent hysteresis a necessity for all good spring materials. Cork fortunately, is also highly resilient and with only a few percentage points of hysteresis when compressed for long periods of time.

FIG. 1 shows that on rebound, i.e., an upwardly traveling piston rod 19, there is only the load, and the metal-to-meta end-stop, R, of the damping tube 16 to stop its upward movement. This applies principally to undamped cylinders. When a high degree of damping is used, this condition is greatly alleviated. In some usage, the cylinder 13 may be full of pressure-free cork and oil even when the piston rod 19 is at full up-stroke. In other cases of high static loading, the cork and oil a few minor changes over the mounting 10 of FIG. 1.

The bottom head. 12A becomes a bottom head common to both the upper cylinder l3U and the lower cylinder 13L. The heat conducting disk 35 is not used and, therefore, the two cork cylinders 17 of FIG. 1 are combined into one long cork cylinder 17. The dual unit is supported by a base 33. The two piston rods 19U and 19L are connected to a common yoke 32. This yoke is of such length that when one piston head is centered in its cylinder, the other head is also approximately centered in its cylinder. The pistons of course move in unison, but opposed in phase. The sprung load may be carried on the top arm of the yoke 32, as shown by the force arrows 30A. The forces 30A are balanced by the reaction forces 31A of the base 33.

To put oil in the dual unit, the piston rod 19L of the lower cylinder 13L is placed in a position of zero intrusion. This, of course, puts the piston rod 19U o f the upper cylinder 13U in full intrusion position. Oil is now pumped into the lower cylinder 13L until all of the air is expelled and it is full of oil, i.e.. the oil space is full. Now, without changing the positions of the piston rod 19U and 19L oil is pumped into the upper cylinder 13U until all of its air is exeplled, whereupon the air escape valve 25 in fitting 24 is permitted to close. Then continuing to pump oil into cylinder 13U, pressure will-de-.

velop within the cylinder 13U and force its piston rod 19U to begin to extrude out of the cylinder 13U. The pumping of oil into the cylinder 13U is continued until its piston rod 19U is at its mid-intrusion position. The device is then ready for operation.

FIG. 3 shows that the lower piston rod 19L is smaller in diameter than the upper piston rod 19U. It will be observed that the weight (load) is supported by the inder 13L is to offer resistance in casepf high energy,

upward rebounds, to prevent a metal-to-metal impact of the upper piston head 28U with itss packing nut re sulting in possible damage and abrupt stops.

In operation, it will be noted that the upward force (it being biased upwardly) on the upper piston rod 19U is the product of its spring modulus and its intrusion x, while the force downwardly on the lower piston rod 19L at that same instant will be the product of its spring modulus and its intrusion L X. Itis desirable that the total force downward when the yoke 32 is full-up, the be double the maximum load weight and when the yoke is full-down that there be a resultant force upward equal to twice the maximum load weight. This is to say that at its full intrusion the lower piston rod 19L has a downward force equal to the load weight and at zero intrusion, zero force. Thus, at mid position of the yoke 32 the upper piston rod 19U must have an upward force equal to the weight,'plus one-half that value, because of the downard force of the piston rod 19L. Hence, the upward force on the upper piston rod 19U at mid-point is 1% times the weight, which means that it is three-times the downward opposing force of lower piston rod 19L. If the cylinder 13U and 13L are identical in size and in cork-oil fill, then this ratio of l to 3 in the spring modulus must be achieved by varying the diameter of the piston rods.

In the computations above, it was shown that the pressure modulus was equal to the product of the composite bulk modulus, the length of stroke and the area of the piston divided by the product of the length of the total piston travel and the area of the cork-oil capacity of the cylinder. Also, the spring modulus is equal to the product of the pressure modulus and the piston area. Therefore, if other factors are kept constant, S varies with the square of the piston area. Consequently, if the area of the upper piston rod 19U is a,,, and the area of the lower piston rod 19L is a,,, then, a 2/3 =Z1 When this area ratio is maintained, the spring modulus of the upper piston rod 19U is just three times the lower piston rod-19L. If the spring modulus of the lower piston rod 19L is S, then the spring modulus of the upper piston rod 19U, is 38, and the force on the upper piston rod is 3SX and the force, on the lower piston rod 19L is downward and is S (L -X). The composite piston rod force is 3 SX S(LX) 4 SX SL.

As an example of the piston forces involved, assume that the cylinders are similar to the ones in the earlier computations. The fill is 70 percent oil and 30 percent cork and K 5,550 psi. The stroke is 1 ft. The upper 30.

piston rod 19U has an area of 3.14 sq. in., and the lower piston rod 19L has an area of 1.81 sq. in. The crosssectional area of oil and cork is 31.4 sq. in. The spring modulus of the lower piston rod 19L is 582 lbs/ft. of intrusion. The upper piston rod 19U has three times this, or 1,746 lbs/ft. of intrusion. The following Table II shows data for various positions of the two piston rods l9U and 19L.

TABLE II Position Upper Piston Lower Piston Wt. total of Equa Force in Equa Force in in force Piston tion lbs. 1 tion lbs. lbs. lbs. Top 35 (0) 0 S(L) S82 82 I164 Center 3S(L/2) 873 S (LIZ) 291 582 0 Bottom 3S(L) I746 5(0) 0 -582+ l 164 It is observed that at the top of the stroke there is a downward force equal to double the weight, hence a 2 g acceleration downward and at the bottom of a stroke there is a like force upward. These forces are over and above any forces due to all-liquid compression in the hole-free ends R of the damping tube 16. It is noted that in this dual unit of FIG. 3 the amount of damping is substantially doubled due to the duality.

Although the embodiments described have used cork as the solid material, there are other special materials which have been-found to be satisfactory for use in the present invention. These other materials have many of the same properties as cork and specifically the important properties of a lower bulk modulus of elasticity than the liquid used, a negative coefficient of temperature, bulk modulus-wise, a closed cell construction and imperviousness to the liquid. Two such other materials I which have been used satisfactorily in the present invention are high and low density, closed-cell, synthetic nitrile rubbers. These synthetic cellular rubbers are commercially available from, for example, Greene resistant rubber compound made from synthetic rubber or rubber-like materials, alone or in combination, for services having specific requirements for resistance to the action of petroleum-base oils or other organic liquids. The SBE 41 material is a low density, expanded closed-cell or nitrile rubber material. The SBE 43 material is a high density, expanded closed-cell nitrile rubber material. Buna N rubbers conforming to the same MIL. Spec. C3133, Types S, SBE 41 and SEE 43 also may be used. Still another synthetic or natural material having a closed-cell construction, a lower bulk modulus of elasticity than the liquid used, and imperviousness to the liquid, may be used in place of cork.

Since certain changes may be made in the above apparatus without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted in an illustrative and not in a limiting sense.

The following claims are written around a cushion mounting to support a load, the normal use of the device, but it will be understood that the cushion mounting does not acually see a load, but only the gravitational force due to a material load. It is the intent that the claims include any reasonable force, or forces, impressed upon the piston rod, no matter how they are generated or transmitted to the piston rod.

What is claimed is:

1. A cushion mounting to spring mount a load and to cushion a load against shock, said cushion mounting comprising:

a housing having means defining a chamber;

a load-mounting member reciprocally supported by said housing and adapted to reciprocate within said chamber, and with the load-mounting end of said load-mounting member extending out of said chamber and said housing, and the said housing being pressure sealed around the said loadmounting member to prevent liquid escape therearound;

said chamber being filled with a liquid-solid composite when said load-mounting member is fully extended; said solid of the said composite being a resilient solid having a bulk modulus lower than the bulk modulus of the said liquid portion of the said composite;

whereby the placing of a load on the extended end of said load-mounting member causes said loadmounting member to intrude into the said compos ite-filled chamber, thereby compressing the said liquid-solid composite volume causing a volume decrease therein, said volume decrease being equal to the intruded volume of the said load-mounting member; and

that quantum of energy required to stop said intruding load-mounting member being absorbed and stored as strain energy in said compressed liquidsolid composite; and said strain exerting a continual extruding force on said load-mounting member; and

that said quantum of stored strain energy being expended on said load-mounting member as it returns to its no-intrusion position.

2. In a liquid spring comprising in combination:

a housing having means defining a chamber;

at lease one load-mounting piston rod mounted to reciprocate within said chamber and extending out of said housing, and with said housing pressure around said piston rod;

said chamber normally being filled with a liquid when said piston rod is fully extended;

whereby when a load is placed on the extension of said load-mounting piston rod it causes the piston rod to intrude into said liquid filled chamber, thereby compressing the said liquid therein, and the volume decrease due to compression being proportional to the magnitude of the load and inversely proportional to the bulk modulus of the said liquid; and that quantum of energy required to stop, and/or support a load, being absorbed and stored as compressional strain energy in th said liquid; and said strain energy exerting a continual extruding force upon said intruded piston rod; and said quantum of energy being expended on said piston rod as said piston rod returns to the nointrusion position;

the improvement for decreasing the spring modulus of said liquid spring, said improvement comprising:

incorporating with the said liquid a quantity of a resilient solid whose bulk modulus is lower than the bulk modulus of the said liquid, whereby the bulk modulus of the composite of said liquid and said resileint solid is lower than the bulk modulus of said liquid, thereby reducing the spring modulus of the said liquid spring by the same proportional amount.

3. The liquid spring defined by claim 2 wherein:

said chamber having a first valve means permitting introduction of said liquid, and a second valve means for bleeding-off gas or liquid.

4. The liquid spring defined by claim 2, further including:

a damping sleeve mounted within said chamber concentrically with said load mounting-piston rod, said sleeve being porous to said liquid, and said resileint solid being disposed about said sleeve, and said load-mounting piston rod adapted to reciprocate within said porous sleeve.

5. The liquid spring defined by claim 4, further including:

said damping sleeve having both ends closed against fluid flow, and further, said damping sleeve having a section at each end that is nonporous, and said load-mounting piston rod extending through one of said closed ends.

6. The liquid spring defined by claim 4, further including:

said load-mounting piston rod having a piston on its intruded end, which said piston being a sliding fit within said damping sleeve.

7. The liquid spring defined by claim 2, wherein:

said chamber having a pressure gauge calibrated in piston rod force units and communicating with said intrachamber liquid space.

8. The liquid spring defined by claim 2, wherein:

said resileint solid having a negative temperature co efficient of bulk modulus, decreasing with rising temperature.

9. The liquid spring defined by claim 3, further including:

the interior of said chamber being prestressed by pumping additional liquid into said chamber through said first valve means to produce the de sired intrachamber pressure.

10. A rebound cushion mounting for spring mounting a load and to cushion said load against rebounds, comprising:

a first liquid spring to spring support a load;

a second liquid spring to snub rebounds of said load, said second liquid spring having a spring modulus lower than the spring modulus of said first liquid spring;

a base to support said both liquid springs;

said first liquid spring mounted on top of said base with its piston rod projecting upwardly;

said second liquid spring mounted on the underside of said base with its piston rod projecting downwardly, to work in opposition to said first liquid spring;

a yoke member mounting said sprung load;

said yoke member spanning both said liquid springs and interconnecting thereto the extended end of the piston rod of each of the said two liquid springs to form a reciprocative, integral, dual-unit;

the said yoke member having a span relationship that when the piston rod of said first liquid spring is at mid-intrusion position, the piston rod of the said second liquid spring will also be substantially at its mid-intrusion position; and

whereby said load supporting first liquid spring and said rebound-snubbing second liquid spring operate as a unit with a phase-reversed relationship, so that the rebound-snubbing second liquid spring serves to reduce the amount of shock that can occur when said load is suddenly reduced, or rebounded.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 5, 77 55 Dated December t, 1973v Invent r( Homer I. Henderson It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column A, line 8, correct the spelling of "momentum";

line 16, change "deviceis" to device is Column 6, line 56, in equation (8) change '1 Z" to l Z line 6 l-, change "5150 ='0.59 2000" to Column 7, line 67, change "trained" to strained Column 8, line 1 T, change "tohe" to to the lineAO, change "destruction" to destructive Column 9, line 55, correct the spelling of "expelled";

line A9, correct the spelling of "its";

line 58, after "full-up" delgte "the" 2 Column 10, line 17, change "a 2/5 a to a5 /5 a Column 11, line 10, change "another" to other Claim 2, line 5, after"'pressure" insert sealed line 26, correct the spelling of "resilient".

- Signed and sealed this 16th day of July 197 (SEAL) Attest:

McCOY M. GIBSON, JR. c. MARSHALL DANN Attesting Officer v Commissioner of Patents FORM po'wso (10459) uscoMM-Dc 60376-P69 U.5. GOVERNMENT PRINTING OFFICE t 1969 O3GG-33l, 

1. A cushion mounting to spring mount a load and to cushion a load against shock, said cushion mounting comprising: a housing having means defining a chamber; a load-mounting member reciprocally supported by said housing and adapted to reciprocate within said chamber, and with the load-mounting end of said load-mounting member extending out of said chamber and said housing, and the said housing being pressure sealed around the said load-mounting member to prevent liquid escape therearound; said chamber being filled with a liquid-solid composite when said load-mounting member is fully extended; said solid of the said composite being a resilient solid having a bulk modulus lower than the bulk modulus of the said liquid portion of the said composite; whereby the placing of a load on the extended end of said loadmounting member causes said load-mounting member to intrude into the said composite-filled chamber, thereby compressing the said liquid-solid composite volume causing a volume decrease therein, said volume decrease being equal to the intruded volume of the said load-mounting member; and that quantum of energy required to stop said intruding loadmounting member being absorbed and stored as strain energy in said compressed liquid-solid composite; and said strain exerting a continual extruding force on said load-mounting member; and that said quantum of stored strain energy being expended on said load-mounting member as it returns to its no-intrusion position.
 2. In a liquid spring comprising in combination: a housing having means defining a chamber; at lease one load-mounting piston rod mounted to reciprocate within said chamber and extending out of said housing, and with said housing pressure around said piston rod; said chamber normally being filled with a liquid when said piston rod is fully extended; whereby when a load is placed on the extension of said load-mounting piston rod it causes the piston rod to intrude into said liquid filled chamber, thereby compressing the said liquid therein, and the volume decrease due to compression being proportional to the magnitude of the load and inversely proportional to the bulk modulus of the said liquid; and that quantum of energy required to stop, and/or support a load, being absorbed and stored as compressional strain energy in th said liquid; and said strain energy exerting a continual extruding force upon said intruded piston rod; and said quantum of energy being expended on said piston rod as said piston rod returns to the no-intrusion position; the improvement for decreasing the spring modulus of said liquid spring, said improvement comprising: incorporating with the said liquid a quantity of a resilient solid whose bulk modulus is lower than the bulk modulus of the said liquid, whereby the bulk modulus of the composite of said liquid and said resileint solid is lower than the bulk modulus of said liquid, thereby reducing the spring modulus of the said liquid spring by the same proportional amount.
 3. The liquid spring defined by claim 2 wherein: said chamber having a first valve means permitting introduction of said liquid, and a second valve means for bleeding-off gas or liquid.
 4. The liquid spring defined by claim 2, further including: a damping sleeve mounted within said chamber concentrically with Said load mounting-piston rod, said sleeve being porous to said liquid, and said resileint solid being disposed about said sleeve, and said load-mounting piston rod adapted to reciprocate within said porous sleeve.
 5. The liquid spring defined by claim 4, further including: said damping sleeve having both ends closed against fluid flow, and further, said damping sleeve having a section at each end that is nonporous, and said load-mounting piston rod extending through one of said closed ends.
 6. The liquid spring defined by claim 4, further including: said load-mounting piston rod having a piston on its intruded end, which said piston being a sliding fit within said damping sleeve.
 7. The liquid spring defined by claim 2, wherein: said chamber having a pressure gauge calibrated in piston rod force units and communicating with said intrachamber liquid space.
 8. The liquid spring defined by claim 2, wherein: said resileint solid having a negative temperature coefficient of bulk modulus, decreasing with rising temperature.
 9. The liquid spring defined by claim 3, further including: the interior of said chamber being prestressed by pumping additional liquid into said chamber through said first valve means to produce the desired intrachamber pressure.
 10. A rebound cushion mounting for spring mounting a load and to cushion said load against rebounds, comprising: a first liquid spring to spring support a load; a second liquid spring to snub rebounds of said load, said second liquid spring having a spring modulus lower than the spring modulus of said first liquid spring; a base to support said both liquid springs; said first liquid spring mounted on top of said base with its piston rod projecting upwardly; said second liquid spring mounted on the underside of said base with its piston rod projecting downwardly, to work in opposition to said first liquid spring; a yoke member mounting said sprung load; said yoke member spanning both said liquid springs and interconnecting thereto the extended end of the piston rod of each of the said two liquid springs to form a reciprocative, integral, dual-unit; the said yoke member having a span relationship that when the piston rod of said first liquid spring is at mid-intrusion position, the piston rod of the said second liquid spring will also be substantially at its mid-intrusion position; and whereby said load supporting first liquid spring and said rebound-snubbing second liquid spring operate as a unit with a phase-reversed relationship, so that the rebound-snubbing second liquid spring serves to reduce the amount of shock that can occur when said load is suddenly reduced, or rebounded. 